Download Protein

Chemistry Comes Alive
Part B
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
2
Categories of Molecules
 Organic molecules
 Contain carbon
 Covalent bonds
 Produced by living or once living organisms
 Inorganic molecules
 Typically do not contain carbon
 Include:
 Water, ammonia, salts, and some acids and bases
Salts
 Electrolytes
 conduct electrical currents
 Examples: NaCl, KCl, CaCl2, Ca3(PO4)2
Acids and Bases
 Acids release H+
HCl  H+ + Cl –
 Bases release OH–
NaOH  Na+ + OH–
Acid-Base Concentration (pH)
 pH describes the concentration of H+ in a solution
 pH = -log[H+]
 A scale based on [H+] found in H2O is used
 H2O  H+ + OHˉ
 [H+] =1x10-7M and [OHˉ] = 1x10-7M
 Therefore H2O has a pH = 7
 Acidic solutions have [H+] higher than 1x10-7M and
therefore a pH < 7
 Alkaline solutions have lower [H+] concentrations
and therefore a pH > 7
Acid-Base Concentration (pH)
 Acidic: pH 0–6.99
 Neutral: pH 7.00
 Basic: pH 7.01–14
Figure 2.12
Buffers
 Solutions of molecules that resist changes in pH
 pH of blood is maintained by carbonic acidbicarbonate buffering system
 Carbonic acid dissociates, reversibly releasing
bicarbonate ions and protons
 The chemical equilibrium between carbonic acid
and bicarbonate resists pH changes in the blood
H2O + CO2
H2CO3
H+ + HCO3ˉ
Organic Molecules
 Unique to living systems - hence organic
 Small molecules & macromolecules (biomolecules)
 Macromolecules are polymers of smaller organic
molecules
 Major biomolecule groups
 Carbohydrates
 Lipids
 Proteins
 Nucleic Acids
Carbohydrates
 Major functions are
 energy source
 support (plants, fungi & bacteria)
 parts of other macromolecules
 Monosaccharides or simple sugars
Carbohydrates
 Disaccharides
Carbohydrates
 Polysaccharides - polymers of simple sugars
 Each monosaccharide is a residue
 Glycogen - energy storage in animals
 Starch – energy storage in plants
 Cellulose – support structures in plants
Figure 2.13c
Carbohydrates in other Biomolecules
 Glycoproteins
 Proteins containing sugar residues
 Glycolipids
 Phospholipids with sugar residues
 Ribose and Deoxyribose sugars as part of
nucleotides and nucleic acids
Lipids
 Representatives
 Neutral fats – triglycerides - adipose tissue
 Phospholipids – chief component of cell membranes
 Steroids – cholesterol, bile salts, vitamin D, hormones
 Vitamins A, E & K
 Eicosanoids – prostaglandins
Fatty Acids & Triglycerides
Phospholipids
Figure 2.14b
Phospholipids in membranes
 Phospholipids make up cellular membranes (lipid bilayers)
Steroid Lipids
Prostaglandins
 Eicosanoids –
 Used to make
prostaglandins
Protein
 Polymers of amino acids
Figure 2.16
Amino Acids
 Building blocks of protein, containing an amine
group, a carboxyl group, & a variable side chain
Structural Levels of Proteins
Structural Levels of Proteins
Structural Levels of Proteins
Figure 2.17d, e
Fibrous and Globular Proteins
 Fibrous proteins
 Extended and thread-like proteins
 Examples: keratin, elastin, collagen, myosin, actin
 Globular proteins
 Compact, spherical proteins with tertiary and
quaternary structures
 Examples: antibodies, peptide-hormones, and
enzymes
Characteristics of Enzymes
 Proteins that are biological catalysts
 Chemically specific
 Usually named for the reaction they catalyze
 Names often end in suffix -ase
Protein Function - Enzymes
 Protein and substrate fit together in a specific way due to Hbonds, ionic bonds and non-polar interactions
Figure 2.18a
Mechanism of Enzyme Action
Active site
Substrates
1
Enzyme (E)
Substrates (s)
H20
Enzymesubstrate
complex (E–S)
2
Free enzyme (E)
3
Covalent bond
Internal rearrangements
leading to catalysis
Product (P)
Nucleic Acids
 Polymers of nucleotides
 Nucleotide is
 N-containing base
 pentose sugar
 phosphate group
 DNA and RNA
Nucleotides – The Bases
Nucleotides – The Sugars
for RNA
for DNA
Nucleosides – Sugar + Base
Deoxyadenosine
Nucleotide – Nucleoside + Phosphates
Nucleic Acids – Polymers of Nucleotides
Structure of DNA
 Complementary base-pairing
 A-T
 G-C
Figure 2.21a
Deoxyribonucleic Acid (DNA)
 Double-stranded helical molecule
 Constitutes chromosomes in nucleus
 Replicates ensuring genetic continuity
 Provides instructions for protein synthesis
Ribonucleic Acid (RNA)
 Contains the base uracil in place of thymine
 Made from a DNA template
 Three major varieties of RNA:
 mRNA – encodes a protein
 tRNA – conveys amino acid to ribosome as directed
by mRNA
 rRNA – joins amino acids together to form protein
as directed by mRNA
Adenosine Triphosphate (ATP)
Source of immediately usable energy
for the cell
Figure 2.22
How ATP Drives Cellular Work
Figure 2.23